Sperm sorting
Encyclopedia
Sperm sorting is a means of choosing what type of sperm cell is to fertilize
Fertilisation
Fertilisation is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo...

 the egg cell. It can be used to sort out sperm that are most healthy, as well as determination of more specific traits, such as sex selection
Sex selection
Sex selection is the attempt to control the sex of the offspring to achieve a desired sex. It can be accomplished in several ways, both pre- and post-implantation of an embryo, as well as at birth...

 in which spermatozoa are separated into X- (female) and Y- (male) chromosome bearing populations based on their difference in DNA content. The resultant 'sex-sorted' spermatozoa are then able to be used in conjunction with other assisted reproductive technologies such as artificial insemination
Artificial insemination
Artificial insemination, or AI, is the process by which sperm is placed into the reproductive tract of a female for the purpose of impregnating the female by using means other than sexual intercourse or natural insemination...

 or in-vitro fertilization (IVF) to produce offspring of the desired sex.

For general health

DNA damage in sperm cells may be detected by using Raman spectroscopy
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...

. It is not specific enough to detect individual traits, however.

The sperm cells having least DNA damage may subsequently be injected into the egg cell by intracytoplasmic sperm injection
Intracytoplasmic sperm injection
Intracytoplasmic sperm injection is an in vitro fertilization procedure in which a single sperm is injected directly into an egg.-Indications:...

 (ICSI).

Methods

Sperm sorting utilizes the technique of flow cytometry
Flow cytometry
Flow cytometry is a technique for counting and examining microscopic particles, such as cells and chromosomes, by suspending them in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and/or chemical...

 to analyze and 'sort' spermatozoa. During the early to mid 1980s, Dr. Glenn Spaulding was the first to sort viable whole human and animal spermatozoa using a flow cytometer, and utilized the sorted motile rabbit sperm for artificial insemination. Subsequently, the first patent application disclosing the method to sort "two viable subpopulations enriched for x- or y- sperm" was filed in April of 1987 as US Application Serial Number 35,986 and later became part of US Patent 5,021,244; and the patent included the discovery of haploid expression (sex-associated membrane proteins, or SAM proteins) and the development of monoclonal antibodies to those proteins. Additional applications and methods were added, including antibodies, from 1987 through 1997 . At the time of the patent filing, both Lawrence Livermore National Laboratories and the USDA were only sorting fixed sperm nuclei , after the Application Serial Number 35,986 patent filing a new technique was utilized by the USDA where "sperm were briefly sonicated to remove tails". USDA in conjunction with Lawrence Livermore National Laboratories, 'Beltsfield Sperm Sexing Technology' relies on the DNA difference between the X- and Y- chromosomes . Prior to flow cytometric sorting, semen is labeled with a fluorescent dye called Hoechst 33342 which binds to the DNA of each spermatozoon. As the X chromosome is larger (ie has more DNA) than the Y chromosome, the "female" (X-chromosome bearing) spermatozoa will absorb a greater amount of dye than its male (Y-chromosome bearing) counterpart. As a consequence, when exposed to UV light during flow cytometry, X spermatozoa fluoresce brighter than Y- spermatozoa. As the spermatozoa pass through the flow cytometer in single file, each spermatozoon is encased by a single droplet of fluid and assigned an electric charge corresponding to its chromosome status (eg X-positive charge, Y-negative charge). The stream of X- and Y- droplets is then separated by means of electrostatic deflection and collected into separate collection tubes for subsequent processing .

Accuracy

While highly accurate, sperm sorting by flow cytometry will not produce two completely separate populations. That is to say, there will always be some "male" sperm among the "female" sperm and vice versa. The exact percentage purity of each population is dependent on the species being sorted and the 'gates' which the operator places around the total population visible to the machine. In general, the larger the DNA difference between the X and Y chromosome of a species the easier it is to produce a highly pure population. In sheep and cattle, purities for each sex will usually remain above 90% depending on 'gating', while for humans these may be reduced to 90% and 70% for "female" and "male" spermatozoa, respectively.

Ethical concerns

For the most part, sperm sorting shares the ethical concerns implicit to the idea of sex selection. However, the fact that sperm sorting is in effect sex-preselection, with the sex of the offspring decided at conception rather than post-conception (preimplantation genetic diagnosis
Preimplantation genetic diagnosis
In medicine and genetics pre-implantation genetic diagnosis refers to procedures that are performed on embryos prior to implantation, sometimes even on oocytes prior to fertilization. PGD is considered another way to prenatal diagnosis...

), post-implantation (ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...

) or post-birth, makes the technique decidedly more attractive from an ethical standpoint.

Regulation

In the US, for humans, the practice of sperm sorting is tightly regulated by the FDA. In effect, it remains an ongoing clinical trial
Clinical trial
Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...

, with the procedure made available to a limited number of participants each month, in addition to fulfilling certain criteria, such as having a disease with sex linkage
Sex linkage
Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of inheritance...

or having at least one child (for family balancing).
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK